Micromechanical Studies of Deformation, Stress and Crack Nucleation in Polycrystal Materials

Abstract

Crystal plasticity analyses of fatigue crack nucleation in an fcc nickel alloy and bcc ferritic steel have been carried out. Three and four-point bend tests respectively carried out on the nickel alloy and steel samples are analysed using a direct representation of the observed microstructures and crystallographic orientations obtained by EBSD. In so doing, direct comparisons of predicted stress, accumulated plastic strain and the independent slip system accumulated slips have been assessed in relation to the location of fatigue crack nucleation. Regions of accumulated plastic strain are found to be precursors to the experimentally observed sites of crack nucleation and propagation in the fcc nickel polycrystal, but for nucleation only in the bcc ferritic steel. For the latter, a decomposition of the accumulated plastic strain in to the major contributors from the independent slip systems show close coincidence of the crack nucleation site with both $\{110\}$ and $\{112\}$ slip and that it is not the case that a single slip system type dominates.